This invention relates to an in situ soil testing device, and particularly a tapered in situ soil testing device for measuring in situ soil stresses and other properties.
Numerous devices have been used for testing the in situ stresses in the soil. One of these devices utilizes a multi-vaned blade which may be inserted into the soil. Strain gauges on the surfaces of the various blades measure the soil stresses or pressures which are exerted on the faces of the blade.
When blades of different thicknesses are used, the soil exerts correspondingly different stresses or pressures on the faces of the blades. Generally, the thicker the blade, the greater the soil pressure, and the thinner the blade, the less the soil pressure. However, in soft soils, a plastic failure may occur causing lower pressures to be recorded on the thicker portion of the wedge. The use of a tapered device, such as contemplated by the present invention, is to accurately define the pressure at which this behavior may occur and to give a multiplicity of data points for defining soil response to continuously increasing thickness of a penetrating wedge.
One method for analyzing the soil stress characteristics has been to insert blades of different thicknesses into the soil. The pressures on the faces of the blades are then measured and plotted on a graph. The X-axis of the graph reflects the blade thickness and the Y-axis of the graph reflects the logarithim of pressure reading obtained.
The points plotted in this manner will generally represent a straight line, which when extended to the Y-axis will reflect the theoretical soil pressure which would be obtained for a blade having zero thickness. This procedure is quite adequate for stiff soils, which exhibit high values of elastic modulus; however, softer soils which may behave plastically at low disturbance may cause problems with data interpretation.
Ideally, then, for testing soft soils, it would be desirable to increase the number of individual blades to generate more data points. However, such an approach involves substantial expense and furthermore does not result in an efficient tool for field use. Thus, the use of a multi-blade device has certain limitations and is not strictly applicable to testing soft soils.
Therefore, a primary object of the present invention is the provision of an improved in situ soil testing device.
A further object of the present invention is the provision of a device which permits the measurement of a plurality of soil pressures with a singular device.
A further object of the present invention is the provision of a device including a wedged surface having a plurality of pressure sensors along its length for reading the various soil pressures exerted on the wedged surface.
A further object of the present invention is the provision of a device giving an optimum number of individual thickness-pressure measurements so as to increase the reliability of the soil pressure readings taken with the device.
A further object of the present invention is the provision of a device which is simple in construction and can be easily used in the field.
A further object of the present invention is the provision of a device which is efficient in operation, durable in use and economical to manufacture.